interactive stacked histograms

Jane Greystoke is marketing director at Floppy Banana International the world's leading fresh fruit supplier.
She is reviewing sales trends over recent years.
She can see that overall sales have changed only marginally, but there are obviously some trends.
Apple sales had been increasing until 1995, but are now on the decline.
But what is on the increase?
Clementines look good, but are their sales any higher in 1997 than they were in 1995?
And what about bananas, it isn't clear whether their sales have been increasing, decreasing or simply keeping steady?

Happily Jane is using an interactive stacked histogram.

Try it yourself.

Click on the coloured banana entry in the key, or one of the banana parts of any of the histogram bars.

Ah! Now we can see.
Banana sales have been increasing slowly but steadily since 1994.
Clicking on the clementines we can see that they too are staging a comeback after several years of decline.

The problem

A stacked histogram allows three judgements: (i) the trends on the total height of the columns, (ii) the proportion of each category within each column and (iii) the trends in the lowest category. The trends, or even inter-column comparisons for any other category is very difficult as the blocks are at different heights.

The interactive stacked histogram solves this problem by allowing different trends to be analysed using the same dynamic graph.
It is an example of a general princple of adding interactivity to existing paper visualisations.